What are the baseline investigations for suspected appendicitis?

Baseline Investigations for Suspected Appendicitis

CT scan with IV contrast is the preferred initial imaging modality for adults with suspected appendicitis, while ultrasound is recommended as the first-line imaging for children and pregnant women. 1, 2

Clinical Evaluation

Before proceeding to imaging, the following clinical and laboratory assessments should be performed:

History and Physical Examination

• Key symptoms to assess:
  • Periumbilical pain migrating to right lower quadrant (RLQ)
  • Anorexia, nausea, vomiting
  • Low-grade fever
• Key physical findings:
  • RLQ tenderness (McBurney's point)
  • Abdominal rigidity
  • Rebound tenderness
  • Psoas sign (pain with extension of right hip)
  • Obturator sign (pain with internal rotation of flexed right hip)
  • Rovsing sign (pain in RLQ with palpation of left lower quadrant) 2, 3

Laboratory Tests

• Complete blood count (CBC)
  • Leukocytosis (elevated white blood cell count) - sensitivity 67%, specificity 80% 4, 5
  • Left shift (elevated neutrophil count) - sensitivity 59%, specificity 90% 5
  • Combined elevated WBC and left shift - sensitivity 80%, specificity 79% 5
• C-reactive protein (CRP)
  • Most specific inflammatory marker (specificity 67%) 4
  • Values >10 mg/L suggest inflammation 2
• The combination of elevated leukocytes, neutrophils, and CRP has a sensitivity of 96% for diagnosing appendicitis 2, 4

Imaging Modalities

For Adults

1. CT Abdomen and Pelvis with IV Contrast

   • First-line imaging modality for adults
   • Sensitivity: 97% (range 83-100%)
   • Specificity: 94% (range 64-100%) 1
   • No need for oral contrast in most cases 1
   • Can identify other potential causes of abdominal pain more common in adults 1

2. Ultrasound (when CT is contraindicated)

   • For definitive results only: Sensitivity 99%, Specificity 95%
   • Including equivocal results: Sensitivity 68%, Specificity 96% 1
   • Less reliable than CT but useful when radiation exposure is a concern 1

3. MRI (when CT and ultrasound are contraindicated)

   • Sensitivity: 96% (range 85-97%)
   • Specificity: 97% (range 89-100%) 1
   • Limited availability and higher cost compared to CT and ultrasound 1

For Children

1. Ultrasound

   • First-line imaging modality for children
   • For definitive results only: Sensitivity 99%, Specificity 96%
   • Including equivocal results: Sensitivity 82%, Specificity 94% 1, 2
   • Avoids radiation exposure 1

2. MRI or CT (if ultrasound is equivocal/indeterminate)

   • MRI: Sensitivity 98%, Specificity 97%
   • CT: Sensitivity 96%, Specificity 96% 1
   • MRI preferred when available to avoid radiation exposure 2

For Pregnant Women

1. Ultrasound

   • First-line imaging modality for pregnant women
   • Limited sensitivity (26%) but high specificity (100%) 1, 2

2. MRI (if ultrasound is inconclusive)

   • Sensitivity: 93% (range 18-100%)
   • Specificity: 96% (range 54-100%) 1, 2
   • Preferred over CT to avoid radiation exposure 1

Clinical Scoring Systems

Clinical scoring systems can be used to stratify patients and guide the need for imaging:

• Alvarado Score components:
  • Migration of pain to RLQ (1 point)
  • Anorexia (1 point)
  • Nausea/vomiting (1 point)
  • RLQ tenderness (2 points)
  • Rebound tenderness (1 point)
  • Elevated temperature (1 point)
  • Leukocytosis (2 points)
  • Left shift (1 point)
  • Score interpretation:
    • 0-4: Low risk (imaging may be deferred)
    • 5-6: Intermediate risk (imaging recommended)
    • 7-10: High risk (surgical consultation) 3, 6

Common Pitfalls and Caveats

1. Do not rely solely on laboratory tests for diagnosis or exclusion of appendicitis. While combined inflammatory markers have high sensitivity, they lack specificity 2

2. Do not omit imaging in women, regardless of clinical presentation, due to overlapping gynecological conditions 2

3. Be aware of atypical presentations in:

   • Children under 5 years (less specific symptoms, higher perforation risk)
   • Elderly patients (blunted inflammatory response)
   • Pregnant women (displaced appendix due to gravid uterus) 2, 7

4. Recognize that appendix visualization rates vary by modality:

   • Ultrasound: Often limited by body habitus and bowel gas
   • CT: Superior visualization in most patients
   • MRI: Good visualization but limited availability 1

5. Consider alternative diagnoses when imaging is negative, particularly in women of reproductive age (ovarian cysts, PID) and elderly patients (diverticulitis, colon cancer) 1

By following this diagnostic algorithm and selecting the appropriate imaging modality based on patient characteristics, clinicians can optimize the diagnosis of appendicitis while minimizing unnecessary radiation exposure and surgical interventions.